1. Field of the Invention
The present invention relates to field emission structures and devices, including field emission-based flat panel displays, as well as to methods of manufacture and use of such structures and devices.
2. DESCRIPTION OF THE RELATED ART
In the technology of field emission structures and devices, a microelectronic emission element, or a plurality (array) of such elements, is employed to emit a flux of electrons from the surface of the emission element(s). The emitter surface, referred to as a "tip", is specifically shaped to facilitate effective emission of electrons, and may for example be conical-, pyramidal-, or ridge-shaped in surface profile, or alternatively the tip may comprise a flat emitter surface of low work function material.
Field emitter structures have wide potential and actual utility in microelectronic applications, including (i) electron guns, (ii) display devices comprising the field emitter structure in combination with photoluminescent material on which the emitted electrons are selectively impinged, and (iii) vacuum integrated circuits comprising assemblies of emitter tips coupled with associated control electrodes.
In construction, the field emission tip is characteristically arranged with the tip in electrical contact with an emitter electrode, and in spaced relationship to an extraction electrode, thereby forming an electron emission gap. With a voltage imposed between the emitter electrode and extraction electrode, the field emission tip discharges a flux of electrons. The tip or tip array may be formed on a suitable substrate such as silicon or other semiconductor material, and associated electrodes may be formed on and/or in the substrate by well-known planar techniques to yield practical microelectronic devices.
Horizontal and vertical field emitter types are known in the art, the direction of electron beam emission relative to the substrate determining the orientational type. Horizontal field emitters utilize horizontally arranged emitters (tips) and electrodes to generate electron beam emission parallel to the (horizontally aligned) substrate. Correspondingly, vertical field emitters employ vertically arranged emitters and electrodes to generate electron beam emission perpendicular to the substrate.
Lambe U.S. Pat. No. 4,728,851 and Lee et al. U.S. Pat. No. 4,827,177 disclose horizontal field emission structures of an illustrative nature.
Tomii et al. U.S. Pat. No. 5,053,673 teaches the formation of vertical field emission structures by forming elongate parallel layers of cathode material on a substrate, followed by attachment of a second substrate so that the cathode material layers are sandwiched therebetween in a block matrix. Alternatively, the cathode material layer can be encased in a layer of electrically insulative material sandwiched in such type of block matrix. The block then is sectioned to form elements having exposed cathode material on at least one face thereof. In the embodiment wherein the cathode material is encased in an insulative material, the sliced members may be processed so that the cathode material protrudes above the insulator casing. The exposed cathode material in either embodiment then is shaped into emitter tips (microtip cathodes).
Spindt et al. U.S. Pat. 3,665,241 describes vertical field emission cathode/field ionizer structures in which "needle-like" elements such as conical or pyramidal tips are formed on a (typically conductive or semiconductive) substrate. Above this tip array, a foraminous electrode member, such as a screen or mesh, is arranged with its openings vertically aligned with associated tip elements. In one embodiment disclosed in the patent, the needle-like elements comprise a cylindrical lower pedestal section and an upper conical extremity, wherein the pedestal section has a higher resistivity than either the foraminous electrode or the upper conical extremity, and an insulator may be arranged between the conical tip electrodes and the foraminous electrode member. The structures of this patent may be formed by metal deposition through a foraminous member (which may be left in place as a counter-electrode, or replaced with another foraminous member) to yield a regular array of metal points.
Copending U.S. patent application Ser. No. 07/846,281 filed 4 March 1992 in the names of Gary W. Jones and Ching-Tzong Sune and entitled "Vertical Microelectronic Field Emission Devices and Methods of Making Same", the disclosure of which hereby is incorporated herein by reference, describes a vertical column emitter structure in which the columns include a conductive top portion and a resistive bottom portion, and upwardly vertically extend from a horizontal substrate. By this arrangement, an emitter tip surface is provided at the upper extremity of the column and the tip is separated from the substrate by the elongate column. An insulating layer is formed on the substrate between the columns. An emitter electrode may be formed at the base of the column and an extraction electrode may be formed adjacent the top of the column.
As described in this copending application, the vertical column emitter structure may be fabricated by forming the tips on the face of the substrate, followed by forming trenches in the substrate around the tips to form columns having the tips at their uppermost extremities. Alternatively, the vertical column emitter structure of this copending application is described as being fabricatable by forming trenches in the substrate to define columns, followed by forming tips on top of the columns. In either method, the trenches may be filled with a dielectric and a conductor layer may be formed on the dielectric to provide extraction electrodes.
In field emitter technology, as exemplified by the structures and devices described in the above-discussed patents, there is a continuing search for improvements, particularly under the impetus of commercial as well as military interest in the development of practical and reliable flat panel display devices. Specifically, there is a need in the art for field emitter displays which are able to operate at low turn-on voltages with high accelerating voltages, in a low power, high brightness mode.
The vertical emitter technology disclosed in the above-discussed Tomii et al. and Spindt et al. patents and the Jones et al. application offers the potential advantages of: low capacitance, high speed operation; self-alignment of gate to emitter elements; and high defect-insensitivity attributable to thick dielectric material between the gate and the emitter backplane. Despite these considerable potential advantages, the fabrication of the vertical emitter devices disclosed in the Tomii et al., Spindt et al., and Jones et al. references are relatively complex, time-consuming, and expensive to fabricate, and accordingly are not highly suitable for commercial mass production.
It would therefore be a substantial advantage in the art, and is an object of the present invention, to provide a field emission structure comprising vertical emitter elements, which is simply, quickly, and economically fabricatable, using conventional fabrication equipment and thin film processing techniques.
It is another object of the present invention to provide a method of fabricating a self-aligned gate and emitter structure wherein the field emitter element has a highly efficient emission control and protection resistance character.
It is a further object of the invention to provide a display panel permitting the use of high voltages to improve pixel size control, brightness, and energy efficiency characteristics of the display.
It is a still further object of the invention to provide a non-lithographic patterning process for fabricating emitter structures.
It is yet another object of the invention to provide a display panel utilizing field emitters in the display as power supplies and circuitry means, in order to minimize the overall volume and cost of the display.
Other objects and advantages of the invention will be more fully apparent from the ensuing disclosure and appended claims.